1. Field of the Invention
This invention relates to a process for the flocculation of particulate solids, especially oil- contaminated particulate solids from completion and workover fluids or hydrocarbon fluids, the separation and removal of oil therefrom, and the prolonging of the useful life of the filter used with these fluids. This invention also has utility in flocculating finely divided solids and fatty acids from "Rule 66" solvents, halogenated hydrocarbon fluids, amine fluids and other gas processing fluids such as potassium carbonate and glycols.
2. Description of the Problems and the Prior Art
Contaminants in brines, such as completion and workover fluids, hydrocarbons and halogenated hydrocarbons disrupt the intended use of these fluids. The presence of small amounts of solids in the completion and workover fluids can directly affect completion effectiveness, and especially well productivity. Amounts as low as 500 ppm of solids in completion and workover fluids can be enough to cause total plugging in perforation tunnels, in channels behind pipe, in gravel packs and in propped fractures. Reduction in production due to plugging can be substantial and can also lead to multiple squeeze attempts required to successfully seal cement channels. In gravel packing and in fracturing, solids from the completion and workover fluid mix with the high-permeability gravel with a resulting mixture of gravel and fine solids which can be even less permeable than the fine solids alone. The smaller particles tend to fill the void spaces between the larger particles so that the permeability of the mixture is almost always less than the permeability of the smaller particulate matter. Thus, very few finely-divided solids are tolerated before the high permeability of the pack gravel is lost. There is a need to remove the finely-divided solids from the completion and workover fluids to eliminate these problems.
There is also a need to remove finely-divided solids from hydrocarbon such as naphtha and olefins as well as halogenated hydrocarbon fluids such as perchloroethylene (PERC). These fluids may contain finely divided solids or fatty acids. Hydrocarbons such as naphtha and olefins produced for the manufacture of polyolefins contain particulate impurities which must be removed before further processing. Processed hydrocarbons such as olefins collect metal and ceramic fines from catalyst or other sources. Halogenated hydrocarbon such as PERC, frequently used in dry cleaning operations, may contain fibers, sub-micron level particulate matter, oils and fatty acids. Although no individual particles may be visible to the naked eye, the presence of a color, such as a brown color in an olefin product, indicates the presence of extremely finely-divided solids. Restoring the olefin product to its clear color requires removal of the fines. Likewise, restoring a halogenated hydrocarbon to useful service requires the removal of particulate matter and fatty acids. There is a need to clean hydrocarbons such as olefins to create saleable product, purified feedstock or storage-ready fluids or to remove fine particles to permit flaring or incineration. There is a need to reduce contamination in halogenated hydrocarbons since contaminants cause the compounds to be discarded thus directly affecting operating costs and creating additional disposal problems as halogenated hydrocarbons are regulated.
It is, accordingly, the primary objective of this invention to fulfill these needs.
In U.S. Pat. No. 3,737,037 which issued on Jun. 5, 1973 to Lee Bone, III, there is described a process for treating drilling mud to remove substantially all of the suspended solids particles to provide a reusable mud. The method disclosed includes the addition of a flocculating agent to flocculate solids of size smaller than 20 microns. The flocculating agents disclosed include polyacrylates, polyacrylamides, polyamines, polyamides, partially hydrolyzed polyacrylamides, methylcellulose, carboxymethylcellulose, alkali metal carboxymethylcellulose, halides of aluminum, iron, nickel, and cobalt, aluminum sulfate, alkali metal aluminate, alum, bentonite, attapulgite, sepiolite, hydrous mica, and kaolin. There is no mention whatever, inter alia, within the metes and bounds of the Bone patent of treating clear brine, such as, completion and workover fluids.
Currently, removal of finely divided solids from hydrocarbon fluids and halogenated hydrocarbon fluids is attempted through the use of conventional filter techniques, if it is attempted at all. Frequently, the source of the problem is not recognized and when it is, the fluid is frequently disposed of as being unfit for further service. This is particularly true with fatty acid contamination.
A second objective of the current invention is to prolong the life of the conventional filter used to filter solid particles from drilling fluids, completion and workover fluids, hydrocarbon fluids, halogenated hydrocarbon fluids and amine streams as well as from other fluids. The speed of filtration and the length of time for a clean filter to accumulate a cake which disrupts flow are limiting factors in the recirculation of drilling fluids and completion and workover fluids. Traditionally, filter mesh size equals the size of the smallest particle to be screened. It is known that, and recent studies have shown that the accumulation of solids or "dirt" in a screen filter form a cake which provides a finer mesh than the original screen itself. Particles smaller than the original screen aperture can thus be retained improving the efficiency of the filter. The cake will continue to build on the filter until it reaches a point of maximum efficiency and then will begin to break down. This is due to the pressure differential created across the screen. The addition of filter aids like diatomaceous earth, while not necessary, can increase the incompressibility of the cake allowing longer filter use before the cake begins to break down. As a result, filters can attain a capturing ratio of 1:10 under certain conditions. (i.e. a 50 micron screen can provide removal of particles down to 5 microns). This allows the use of a less expensive larger mesh filter. The limiting factor associated with filter use continues to be the speed of filtration, the length of time before the cake begins to break down, and the presence of oil in the filter cake causing a disposal problem. This is true for hydrocarbon fluid and halogenated hydrocarbon fluid filtration as well as completion and workover fluid filtration. It is an objective of this invention to prolong the life of the conventional filter and address these limiting factors.
A further object of this invention is to separate oil from finely divided solids in the completion and workover fluids and to separate oil from those larger solids which will be or already have been separated from the drilling fluid or completion and workover fluid through conventional means such as shakers, which are vibrating screens canted at an angle from the horizontal, and centrifuges. These oil-contaminated solid particles are produced as a part of the drilling process and create an environmentally-sensitive disposal problem.
In rotary drilling, as practiced in oil and gas exploration, a well bore is formed which extends downwardly from the earth's surface to an oil or gas producing stratum. Formation of the well bore requires cutting into the earth with a rotating bit attached to the end of a drill string formed from joints of pipe sequentially attached as the well bore is extended downwardly. Various fluids are employed in a well bore formations, as for drilling, completions and workover operations. Exemplary of these are (1) drilling fluids, or "muds", which are clay-based, and (2) brines which are clay-free, clear, heavy (dense) fluids. Drilling fluids, or muds, are generally circulated during the drilling process and clear fluids or brines are most often used for well completions and workovers. By definition, a workover is any operation in the well bore other than primary drilling. By this definition, completion operations comprise the first "workover".
In drilling the well bore, generally a clay-based or synthetic drilling fluid, or mud, constituted of a mixture of weighting materials, clays, chemicals and water or oil, is pumped downwardly through the drill string as the well is drilled to exit through jets in the drill bit at the bottom of the hole, the mud ascending to the surface via an annular space between the exterior wall of the drill string and the wall of the hole, or well bore, which may be walled with well casing. At the surface, the mud is pumped to a shale shaker equipped with one or more layers of vibrating screens of one to three, or more mesh sizes for drill cuttings removal. The mud, after removal of the drill cuttings, is then returned to a mud pit where it is temporarily stored for reuse. The drilling fluid, or mud, or brine if it is used in drilling operations, serves several essential functions, the most important of which is to (1) control subsurface pressures and maintain stability, (2) cool and lubricate the drilling tool or bit, (3) suspend and transport to the surface all movable solids, notably drill cuttings, (4) provide rheologically-stable flow or circulation for the purposes characterized in (2) and (3), supra, and (5) to provide a chemically stable or compatible chemical environment within the well bore. The chemically stable environment will minimize or eliminate corrosion of the drill string and casing as well as provide a compatible environment to the formations encountered in order to seal off permeable formations of oil, gas or water as the well is drilled through different subterranean formations and strata. In the event of a shutdown in the drilling operation, the purpose of the mud, or brine if used in drilling operations, is to hold the cuttings, sand and other solids particulates, or residual solids materials in suspension within the column of drilling fluid while efforts are being made to maintain or restore circulation of the drilling fluid. These oil-contaminated solids, once removed from the drilling fluid or the completion and workover fluids, must be made environmentally safe before disposal.
In drilling operations, the drill cuttings when brought to the surface and separated from the mud, are contaminated with oil. Residual mud solids recovered from the mud pit may likewise be highly oil-contaminated. In fact, at one time it was highly desirable to use oil based muds comprising various solids mixed with diesel oil, e.g. typically 1 to 15 percent by volume diesel fuel, for torque reduction or viscous drag reduction on the drill string to suppress or prevent sticking of the drill string. This very useful practice, once common, is not now often used because of the oil contamination and oil-slick problem. Oil contamination of these solids, particularly the drill cuttings, presents a pressing disposal problem since the solids, when contaminated, cannot simply be dumped. This means, of course, that diesel oil is rarely ever added to muds solely for lubrication purposes, despite the advantages. Instead, more expensive mineral oils are used in oil-based muds on a permit basis. There is a pressing need for processes suitable for decontamination of the oil- contaminated solids so that they may be discarded or discharged without causing pollution of the environment. Also, there is a need to decontaminate the completion and workover fluid as well as the drilling fluid and a need to clean up the produced waters used in drilling a well.
It is, accordingly, a further objective of this invention to fulfill these needs.
In U.S. Pat. No. 4,599,117 which issued Jul. 8, 1986 to the current applicant, S. Roy Luxemburg, there is described a process for decontaminating the oil-covered particulate solids by admixing the same with an aqueous polymeric solution, specifically water-soluble polyacrylamides, and a filter aid, preferably diatomaceous earth. The oil and solid particles are separated, the oil being removed with the aqueous polymeric solution. The oil is then recovered from the aqueous solution and the decontaminated solid particles are available for disposal. The use of polyacrylamides is restricted to temperature ranges at the surface of up to only 150.degree. F. or to short-term use before the polyacrylamide begins to break down.
In U.S. Pat. No. 4,451,377 which issued on May 29, 1984 to S. Roy Luxemburg, there is described a process for cleaning oil-contaminated well bore fluids, including brines and muds. After service, the drilling fluids or muds are often highly contaminated with oil as well as residual solids. Brines eventually become sufficiently contaminated with solids and oil that they are unfit for further use. Oil must also be separated from water from the well and such produced waters decontaminated prior to its disposal. The oil-contaminated brine, after removal from the well bore, is admixed with an aqueous polymeric solution, specifically water-soluble polyacrylamides and the admixture filtered.
A further objective of the current invention is to reduce the surface area of solids in the well bore to aid in carrying solids up from the producing zones by the drilling fluids or the completion and workover fluids. Finely divided cuttings remain in the production zone due to their size and surface area. This causes problems as described above when completion and workover fluids gather finely divided solids. The drag coefficient of the particles must be increased to allow these solids to be carried up and out of the well. Again, the polyacrylamide solution is restricted to lower temperatures and short-term use before the compound begins to degrade.
A further objective is to clean the macro-objects in the well. Build-up of solid particles adhering to the casing, drill pipe, production tubing and other equipment reduces efficiency. The well must be washed to remove particulate matter from casings and other macro objects.
A further objective is to clean contaminated or "spent" amines by flocculating finely divided solids and fatty acids from amine fluids and other gas processing fluids such as potassium carbonate and triethylene glycol, often admixed with diethylene glycol. In particular, it relates to a process for the reconditioning and recovery of contaminated or "spent" amine streams, as used by the gas treating industry in the removal of acid gases from manufactured gases and gaseous process streams, as well as glycol streams to remove excess moisture, and potassium carbonate to remove carbon dioxide.
Amines have been used for the removal of acid gases from manufactured gases and gaseous process streams for many years. For example, the gas stream from which the acid gas is to be removed is pressurized in a contacting tower, or contactor, to physically dissolve under pressure the acid gases, e.g. H.sub.2 S, CO.sub.2, SO.sub.2, RSH and COS. The gaseous stream is then counter-currently contacted with the amine to scrub out the acid gases. Typically, alkanolamines have been used for this purpose, including, among others, diethanolamine (DEA), ethanolamine (monoethanol amine, or 2-aminoethanol) (MEA), n-methyl diethanolamine (MDEA), diisopropanolamine (DIPA), and diglycolamine (DGA) as well as mixtures of amines. Typically, the contaminated amine stream is thermally regenerated by pressure reduction in one or more stages. Inert stripping vapors are sometimes supplied to the regenerator to increase the efficiency of the regeneration.
In conducting an operation of this type, typically a rich liquid amine stream from the bottom of the contactor is heated in a rich-lean amine exchanger and then flashed at reduced pressure to remove part of the acid gas. The partially stripped solution is then passed to a stripper tower and denuded of acid gas by steam stripping. The acid gases are concentrated in an overhead accumulator and then disposed of by burning in an incineration device, e.g. a flare. Lean amine solution from the bottom of a reboiler is exchanged with rich amine in solution exchangers, and then pumped back to the contactor to complete the process loop.
The constant use of a clean amine solution is absolutely essential to the success of a gas treating operation. However, in spite of the use of side stream filters and re-boilers, invariably a point is reached when the amine becomes too dirty, too contaminated, and generally too corrosive for further use in the process. The amine solution at this point has the appearance of a very dirty, viscous black liquid and has been found to contain, inter alia, iron sulfide due to the reaction of H.sub.2 S with the iron of the gathering system, iron hydroxide formed at the higher pH produced by the amine stream when FeS contacts water, saturated fatty acids, generally normal, straight- chain fatty acids containing carboxyl groups capable of reacting to form soaps, and oils used as lubricants in the process, viz. compressor lubricant. It has been reported that some success has been achieved in thermally reclaiming certain contaminated amines via batch distillation in side stream, or slip stream reclaiming operations. However, the high boiling point amines, generally the most useful of the amines, cannot be reclaimed; notably diethanolamine and amines higher boiling than diethanolamine. With these amines, recovery is offset by thermal degradation of the amine as the distillation temperature is increased.
The presence of contaminants in the amines stream reduces the sorptive capability of the amine stream making it less effective as it is returned to contact the sour gas. This leads to replacement of the amine which directly affects operating costs. Amines contaminated with FeS and H.sub.2 S are considered hazardous waste due to their corrosive and poisonous nature. This causes a disposal and transportation problem. Amines solution contaminated with fatty acids form an amine "soap" upon contact with the sour gas stream. This results in much lowered surface tension, allowing amine solution to easily migrate to the succeeding stages and producing disruptive foaming and bubbling. Finally, the carbon-block filters in line with the coalescers plug easily with FeS. Filtering the contaminated amine through a diatomaceous earth filter followed by a 0.5 micron, beta-rated cartridge filtration system showed little difference in the relative color of the fluid which indicates contamination. No difference in the surface tension was detected as measured with a DuNuoy Tensiometer. Current filtration technology does not remove the finely divided grounds and fatty acids from amines. There is a need to remove contaminants from amine streams so these amines can be reused, thus reducing operating costs. There is also a need to remove contaminants from amine streams to increase effectivity of the amines in service and to avoid a hazardous disposal problem. There is a need to remove particulate matter in amines to avoid plugging of the filters.
It is an objective and feature of this invention to address all of these needs and to provide a process for cleaning an amine, or amine solution which has been used in an acid gas treating operation to the extent that it has become too dirty, too contaminated, and often too corrosive, for continued effective use in an acid gas treating operation by flocculating finely divided solids and fatty acids from amine fluids. It is a further feature of this invention to allow the regeneration of the amine stream to take place on-site thus avoiding transportation problems. It is a further feature of this invention to reclaim the contaminants for resale as the contaminants are themselves valuable commodities.
A further objective of this invention is to clean glycol solutions of finely divided solids and fatty acids. Ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG) and proprietary glycol mixtures are used as drying agents in gas processing plants and refineries. Typically, reservoir volumes equal to those of amine sweeteners are required for production purposes. Glycols suffer from the same difficulties as amine streams in that they become contaminated with fine particulate matter and fatty acids. When the fatty acids contact the amine stream, "heat stable amine salts" or soaps are formed. This reduces the surface tension of the solution producing the deleterious effect of foaming and bubbling as well as allowing migration of amines into and through succeeding stages. The presence of fatty acids or "soap" in the glycol solution reduce the ability to dehydrate the gas stream thus causing glycol to eventually be discarded. Due to the nature of the contaminants, these contaminated glycols are considered hazardous which further increases the difficulties associated with transportation and disposal. Also, the presence of particulate matter and soaps in the glycols causes the cartridge filters normally used to suffer from plugging and coalescers to fail.
There is a need to remove the fatty acids and particulate contaminants from the glycols to prolong the use of the glycol stream. There is also a need to clean glycols of hazardous materials to minimize the difficulty associated with transportation and disposal. There is a need to prolong the life of the cartridge filters.
It is an objective of this invention to meet these needs concerning the cleaning of a glycol stream.
A further objective is to clean safety solvents, such as "Rule 66" solvents. Rule 66 solvents are those which meet the California regulation "Rule 66" relating to their safe transportation. This regulation relates to the flash point temperatures of volatile organic solvents, "safety solvents" having a relatively higher flash point as measured by both "closed cup" and "open cup" testing. Volatile Organic Components (VOC's) are regulated both because of their potential contribution to air pollution but also based on their safety in transportation. Examples of such Rule 66 Solvents include PURESOLV.RTM., a registered trademark of the PURESOLV Co., SAFETY KLEEN.RTM., a registered trademark of the Safety Kleen Corp., naphtha and varsol. Contaminants in used Rule 66 solvents generally include fine particles of clay and siliceous materials as well as hydrocarbons (oils) as diluents and fatty acids. These contaminants reduce the useful life of the compound causing it to be discarded. This directly affects operating costs and creates an additional disposal problem since disposal of such fluids is regulated. Currently, filtration is used to remove particles. As with other fluids containing finely divided particles, filtration suffers from plugging of the filter media. The filter also limits the smallest size of the particle which can be screened out of the liquid. There is a need to remove finely divided particles from solvents and to extend the useful life of filters used in this service.
It is an object and feature of this invention to flocculate the finely divided solids in solvents to create flocs which can easily be removed using conventional techniques such as filtration.
In summary, it is the object of this invention to provide a process to flocculate finely divided solids suspended in completion and workover fluids as well as in hydrocarbon fluids, including halogenated hydrocarbons. Fatty acids are also removed in this process. It is also an objective to substantially prolong the life of filter cartridges used to filter completion and workover fluids as well as other fluids. Further objectives are to provide a process for separating oil from finely-divided solids in the completion and workover fluid and from larger solid particles, and to provide a process for cleaning the oil-contaminated completion and workover fluids and produced waters. Additional objectives include forcing finely divided solids from the production zone to the surface and washing the solids from macro objects in the well bore. Objectives also include the cleaning of amines, potassium carbonate, glycol solutions and solvents of particulate matter, fatty acids or oils.